I end up in similar situations, the codebase I work on demands a level of professionalism opus5.5 can't muster on the first pass. Code review remains the bottleneck. Usually I approach it like a code review, reading through and as I find things I markup the code, then afterwords I have the agent collate all the feedback and we discuss and it re-implements. Usually I can simplify and improve a lot in like 3 passes.

One thing that speeds up the reviews and improves my ability to find issues and provide guidance is having the agent work on better review guides (think an html page rendered locally, with object diagrams, decisions/assumptions, animations of data flow if it makes sense, whatever). Those in hand I can read the codebase faster and talk against that document too. I think the end result is better code than I could previously write by hand, in probably 5x the speed.

Usually I can't do more than two projects in parallel though.

Yeah, that makes a ton of sense, I'm going to try this - I particularly like the idea of making animations of data flow.